How to save hot water at home

Q With regard to the impending drought conditions, our hot water supply has to travel a long way to reach the kitchen sink and we seem to be wasting about three to four litres before we get hot water at the tap.

I have read about tankless instantaneous water heaters and was wondering if these would work when connected to the hot-water pipe to heat up the water in the pipe before the hot water arrives.

Will the arrival of the hot water switch the heater off? My main aim is to save water.

A If you use a lot of hot water regularly, then one option would be to fit electrical trace heating tape to the hot-water pipe run, with a controlling thermostat. Covered with thick foam sleeve insulation, this will keep the water in the pipe at whatever temperature you choose. When you turn on the tap, you will get “instant” hot water from the pipe, while water from the hot water cylinder flows in behind it. The trace heating will then only switch on to maintain the pipe temperature at the set level.

The only problem with this is likely to be accessing the pipe along its whole length, if it runs below floors or behind kitchen cupboards, for example. The trace heating tape ideally needs to be fitted in one continuous length, and also insulated along its whole length.

For occasional hot-water use (or if your hot water comes from a combi boiler), a better solution would be an electric under-sink water heater, such as an Ariston 10-

or 15-litre unit. There is no point feeding this from the hot-water supply, because by the time you have turned the tap off (after rinsing a plate or washing your hands, for example), the hot water from the cylinder will simply have filled the pipe run, and will then cool down, thus wasting energy. And with a combi boiler system, the boiler will have fired up, using gas or oil, only to push the cold water sitting in its heat exchanger through into the pipe.

So disconnect and cap-off the hot pipe under the sink, and connect a “T” joint to feed the heater from the cold water pipe, and thence to flow to the hot tap.

I am obliged to advise you that trace heating should be fitted by a registered electrician. Under-sink water heaters can be plugged into a nearby power socket, but should still be installed by a qualified plumber.

CAVITY WHERE THE INSULATION USED TO BE

Q I live in a three-storey block of flats built to a good standard in 1967. Eight years ago we had the cavity walls insulated with a fibrous material blown in through holes drilled in the external brickwork.

Recently two ground-floor flats had timber windows replaced by PVC-U windows and I took the opportunity to inspect the cavity. To my surprise, I noticed that all the insulating material had sunk to the bottom, leaving the cavities as empty as when they were built. Is this to be expected?

BH, York

A Yes, this is very much to be expected. Blown mineral fibre insulation collapses under its own weight, and after a few years it is quite likely to have sunk to the bottom of the cavity. The manufacturers and installers say this cannot happen, of course, and their trade body claims that problems are reported in only a tiny percentage of homes whose cavities have been filled. But this is because nobody ever returns to a job to inspect a completed installation. Cavity wall insulation is a classic “out of sight, out of mind” process.

I would bet that if a routine inspection were to be made of blown mineral fibre installations that were 10 years old or more, 100 per cent of them would be found to have partial or total slumping of the insulation material.

The good news for you, if you live on one of the upper floors, is that your cavities will probably now be almost clear, and you will not be troubled by the dampness problems that are a common result of filling cavities with this material.

The residents in the ground-floor flats might not be so lucky, however, as any moisture in the cavities will be absorbed by the insulation slumped at around skirting-board level, and might start to show through as decorative staining on the inside. Needless to say, none of you will be gaining any heat-saving advantage from the non-existent insulation.